Electrical conductor.



M. HOCHSTADTER. ELECTRICAL couuucma. M'PLlCATlON FILED NMLZ'I. HUB-1,199,789, Patented Oct. 3,1916.

INVENTOR M flochst t M Y y 4ATT0RNEY WITNESSES Ego STATES PATENT OFFICE.

MARTIN HOCHSTADTER, OF HARRISBURG, PENNSYLVANIA.

ELECTRICAL CONDUCTOR.

siding at Harrisburg, in the county of Dauphin'and' State ofPennsylvania, have invented newand useful Improvements. in ElectricalConductorsof-which the followis aspecification. Y f a "is inventionrelates to improvements in electric conductors, and more particularly"to high-tension cables for electric power transmission. i

It is the ob'ect of this invention to pro- 1 yide a c'a-blea apted' tobe laid underground that will be'free of internal sparking and glowingso as to V be safe for use in-very hat such an improvement is necessary,mayb e iealized from the fact, that,-a's yet,

underground power-transmission is used only up to a voltage of about25,000 volts,

. while; electrical machinery and overhead transmission are worked ashigh as 130,000

volts; cable isalead-sheathed cable, and it 'is be cause "undergroundservice practically alivays requires the use of lead-sheathed cablcsthat the difiiculty to which my invention is-directcd is particularlyapplicable to underground cables, In making iristallation of alead-sheathed cable it is necessary to-subject the-cable to greater orless bending, and such bending incident to installation tends; to adisplacement of the insulation and 'the formation of air spaces withinthe insulation itself, between the insulation and the lead whichsurrounds it, and be-.

' tween the insulation and the conductor compressible and inelastic, andwhile easily rounds. Displacement of insulation and.

which it surrounds. The sheath'of the leadsheathed cable is necessarilyof substantial thickness, the lead itself is practically indeformed, itis practically impossible when once it has been bent to bring it backagain to its original shape making contact at all points with theinsulation which it surthe formation of air spaces mean the crea' tionof places where sparking and glow ng may occur to effect the ultimatedestruction of thecable most perfect dielectric. The unshcathedsinthickness an Almost invariably the underground.

Specification of Letters Patent. I P t t g t. 3, 1916. Application nian'areh 27,1913. Serial m. 757,181.

gle cored cable, therefore, is sueha structure that, if the lead'sheathcould beapplied and maintained as an envelop of perfect symmetry andcloseness-of fit, all the re quirements of a structurally perfectcondenser would be had; The troubles which arise with lead-sheathedcables as now made when used for high voltages are-due to two faults intheir construction.

second, cially for polyph'a-se p ower cables, the llinglof the spacesbetween the coreswith an inferior insulating material, usually jute.

The lead sheath ash-l1 external mechani- 'cal protectin cover'mu'st'beof considerable however closely it be pressed upon the cable body, thelimitations upon manufacture are such that vas. a'inatte'r .of fact itfits upon the cable body rather loosely. Indeed, it is thought-desirableby some engineers, -particulaprly in foreign I U First, the" usual wayof applying the lead sheath and,

countries, to consciously provide for n certainlooseness of fit inthis-regard in order to, facilitate bending. In the cablesof usualconstruction transverse plaitsand grooves are during manufactureunavoidably produced on the inner surfaceof the lead cover and the outersurface of the otherwise nude cable, the size of which dependsupon'different circumstances, for instance, the thickness of theinsulating material, the

pressure used/in shaping it, the pressure used in applying the irontapes of the armor (when employed), the thickness of the layer of jutebetween the lead :sheath and the armoi-,'etc.

On account of'conditions of manufacture just explained, and theconsequent structural deformation when once the cable has been installedunder ordinary service conditions which involves its bending, the leadsheath cannot practically fulfil to perfeee tion its second functionadditional -to its.

function as a protecting cover -that,

namely, of anoutside electrode.

Free spaces are liable to occurbetween the lead sheath and the surfaceof the insulating material, the effect of which when present isotherwise would be limited by the-lead sheath) is limited to the outersurfa'eeof the.

insulation by the piesence zit-that point of a separate and closelyadhering thin layer' of electrically conducting material.' Thisinetallizing of the surface of the active ii'isu lation isconvenientlyaccomplished when the outmostlayer ofthe compounded paper insuhition'isbein'gapplied, thereby forming -a' structurally perfect condenser, .theper-' an electrically conducting cylindrical layer as a substantiallyintegral part of the insulation. WheiiZthe,metalliclayer is not indirect contact with the lead sheath, both. layer and sheath should be,grounded. If the lead sheath'i's grounded then the metallic layer willform an electrode ada )ted to carry the same; potential as the eadslieath 5 3 The copper'core, the insulating material, and the metallizedsuiface of the same form fection being eserved even though the cable besubjected to bending, and the cable will be free from sparking andglowing.

The practice of carrying out of this invention'inay be accomplished indifferent ways: For instance, the metallic layer can be formed of tapesof tinfoil .or of very fine wire netting, the thinner the layer thebetter. It is advantugeous to apply this. metal.

lie-tape together with and inserted between the outmost wrapp'ings ofvthe paper as they are laid on; it may however, itself form the outmostlayer, if means nreprovided to secure its perfect adherence to theinsulation. Moreover, it 'is possibleto so prepare .the outerwrappings'of the insulation beforeliand, as to make them in themselveselectrica'lly conducting.

In making underground installation, care should be taken that the thinmetallic layer of the nature and structure indicated shall notconstitute an isolated and continuous.-

conductor for long distances, for it is notdesigned to carry heavycurrents, such, for instance, as short-circuit currents. At the junctionboxes, therefore, the electric continiiity of the layer should beinterrupted, or electric'connection should be made between the layer andthe cablesheath.

A singlecored cable manufactured in accordance with the above invention,representsstructurally a practically perfect condenser. As regardspolyphase cables, the difficulties attendant upon the transmission ofhigh-tension currents are (in the absence of my invention) very great;for in the making up of the cables the individual cores, when insulated,are bunched. the interstices filled with jute in such manner as to buildout to cylindrical form; upon the body so built out with ute, otherinsulation (usually paper \vrappings) is applied; and upon thiscylindrical body the sheath is app lied. In

this relatively coarse filling, spaces are unavoidable, wheredestructive "sparking and glowingwill begin. But the difficulties ofthis character in the use of polyphase cables are greatest at the endsof each .cable section, that is in the unction boxes or joints,

where the conductors of tliecable have'tobe spread in order to makeconnections. The

space around and about the Severalconduca 8 5 tors in the junction-box,shows every intensive electrical discharge at voltages above a certainlimit. 'This condition, existing where joints are required,as-iirjilnct'ion bpxesand i in terminals, is the cause ,of a 'greatdifiiculty for the engineer.

The disturbance inithe electrical field at); the places of joiningiasdescribed above, is f an unavoidable consequence ofthe'presentconstruction ofthese cables, becausein them the internal polyphaseelectrical field isspread all overthe non-homogeneous cross-- section,including. the jute. f, It is obvious that the electrical field Changesiifforn sud denly at the joints where the covers and the jute areremoved and. the conductorsspread;

and that the electric field which, in the sound cable passes through thejute, now

passes through air. Conditions are. disturbed, electrical tension islocalized and intensified, and glowing and breaking down of insulationfollows.-

A phenomenon similar to the abovc occum inside of the polyphase cables.On account of the non-homogeneous cross-section and the electricaltangential strain produced on the surfaces between the close wrapped orprimary insulation and the jute, discharges tain limit. The effect ofthese discharges is similar to that described above, In the usualpolyphase cables, the 3 internal dis-.. cha-rgetends to make the outersurfaces of,

the separately insulated conductors e'q'uipotential, the actualpotential tending'to' becomethat of the neutral or ground, thusrendering theinsulation applied eyes the separately insulated conductorsfree from electrical strain and therefore inactive, and thereforefutile. 7 i

As a. consequence of the faults of the pres- I are brought about atpressures above a cerent construction of 01 base cables, in

P yg

many cases single-cored ca les have heretofore been preferred for veryhigh working .130

pressures.

Since the jute and outside insulation are by the above mentionedtroubles rendered inclfectivv throughout the usual polyphase table. thefaults of the cable are to be over tolllt by avoiding all electricalstrain in these parts by adequate construction.

According to the present invention, this aim also is reached in the mostsimple and thorough way, by applying anouter electrode, as describedabove, to the surface of the insulation of eachindividual conductor. Themethod of inserting, the effect of, and all details of, this electrodeare in accordance with the above-given explanations.

Such a cable now represents electrically three single-cored cablesinclosed in one common lead sheath; and the electrical strain is,therefore, the same for each conductoras for a single-cored cable.Therefore, the effect of such that a polyphase cable will be as reliableas a single-cored cable. At the same time, it is evident that all thedifliculties which now exist at the jointsand terminals of polyphasecables will be eliminated by the new construction.

Other advantages afforded by. this new construction of polyphase cablesare as follows: The common outside insulating ma:

terial surrounding the bunched conductors which is not active and whichis called the belt insulation may be replaced by-a cheap non-impregnatedtextile, or, may be omitted entirel Finally, by using conductors ofsector arm, the jute or filling material might alsobe dispensed with.This latter construction. is very likely to be the cheapest and mostadaptable for such underground cables.

While the preferred forms of this invention areillustrated upontheaccompanying sheet of drawing, yet it is to be understood that minordetail changes may be made with out departing from the scope thereof.

Figure 1 is a view in transverse section taken through a single-coredcable constructed in accordance with this invention. Fig. 2 is a similarview through one form of a three-cored cable illustrating one applicaFig. 3 is 8.-

tion of this invention thereto. view similar to Fig. 2, illustratinganother form of the application of this invention, Fig. 4 is a similarview illustrating the application of this invention to sector-shapedcores and insulation. Fig. 5 is a fragmentary view in transversesection, illustrating a condition under which the advantage of myinvention is realized.

Fig. 1 represents a single-cored cable manfactured in accordance withthis invention and is structurally a substantially perfect condenser.The copper conducting core 1 is surrounded by spirally Wound comundedpaper insulation 2. This layer of insulation will, as will beunderstood, be

a construction is such of such depth as is suited to the intensity ofthe electrical field produced by the core of the size in hand whencarrying a current of intended voltage. The electrically conducting filmor surface 3 of the tinfoil or wire tape is preferably applied to theouter surface of the compounded paper insulation by vinding a strip ofthe same between the spirals of the compounded paper insulation astheoutermost portion is being laid on.

This metallic integument, so applied, will adhere tightly to the compactinsulation and form a substantially integral outer surface thcrefor. Thelead sheathing 4: is preferably provided with a protecting armor 5 ofany recognized form. The bending of the cable will in no way disturb thecompactness of the compounded paper insulation about the core and, asthe metallic surface thereabout forms a substantial integral'partthereof, noair spaces will be formed in the insulation, and the contact"between the metallic surface and insu- .lation will remain perfect.Therefore, as the electric field about ,the copper core is limited bythe metallic film to the outer surface of the insulation, such airspaces as 6 in Fig. 5 formed by imperfect contact between the outer leadsheath 4 and outer surface of the insulation 2 (otherwise underelectrical tension, and places of sparking and glowing) are withouteffect, to injure the cable.

Fig. 2 illustrates a three-cored cable in which each conducting core 1is surrounded by compounded paper insulation 2 and the three insulatedcores surrounded by cylindrical compounded paper insulation 2 providedon its outer surface with the electrical conducting film or surface 3,as described in connection with Fig. 1. The spaces between the coreinsulation 2 and the surrounding cylindrical insulation 2 are filledwith-loosely packed material 7, such as jute. 4

Fig. 3 illustrates a three-cored cable particularly-adapted forpolyphase high-tension transmission, in which each core is pro videdwith the compounded paper insulation and surrounding metallic surface,similar" to that described in connection with Fig. 1. The lead sheathingand armor are placed about the three cores and the spaces therebetweenfilled with loosely packed material such as jute.

Fig. 4 illustrates a modified form of the construction of Fig. 3,inwhich the filling of insulating material between the cores and leadsheath is dispensed with by forming each core and surrounding compactinsulation in sector shape.

I have described as alternative forms of the metallic integument,tinfoil and'fine wire netting. I do not intend to limit my invention toeither or to both of these forms of metal layer, but I mention them asin stances of proper nature and character and easy of application. It isdesirable that. this metallic integument, while substantiallycontinuous, shall still be permeable ,by insulatneath the metallicintegument.

By the phrase a source of high tension current, used in certain of theensuing claims, I mean to characterize a generator and transmitter, orequivalent apparatus, for producing a current of a potential of 10,000volts and upward, and by the phrases hightension cable and high-tensioncircuit I mean to characterize cables and circuits capable' of carryingin economic manner currents having potentials of 10,000 volts andupward.

I claim as my invention:

1. A high-tension cable free from sparking and glowing including in itsstructure a conducting core, a surrounding body of insulating material,a thin layer of conducting material applied to the said body ofinsulating material to the exclusion of air pockets, the continuity ofsuch layer as an isolated conductor being destroyed at intervals.

2. A high-tension cable free from sparking and glowing; including in itsstructure a conducting core, a spirally wound surrounding materialapplied to the said body of insulating material to the exclusion of airpockets, :1 wrapping f securingmaterial surrounding said thin ayer ofconducting material, the continuity of the said thin layer as anisolated conductor being destroyed at intervals.

MARTIN HOCHSTADTER. Witnesses:

ALFRED G. WORMBER,

LANGDON Moons.

